This invention relates generally to the alignment and fixation of bone segments as required for appropriate bone healing, for example after fracture or surgical intervention, and specifically to a device, and the tools needed to install the said device, for the alignment and fixation of cranial bone fragments.
In cases of bone fragmentation where bone fixation is desired, the appropriate alignment of the bone is also a desired result. This is especially true in the cranium, where bone fragmentation can occur as a result of trauma, congenital deformity, or of surgical intervention. In the field of neurosurgery, cranial bone fragments are frequently cut and removed to create defects to allow for access into the cranial cavity and the brain.
The bony cranium is generally regarded to have two surfaces: the outer surface which is characterized by the outer cortex of the bone and is adjacent to the scalp and soft tissue; and the inner surface which is characterized by the inner cortex of the bone and which is adjacent to the cranial cavity and the brain. Between the inner cortex and the outer cortex, which are dense layers of bone, lies the diploe which generally consists of soft bone and bone marrow. When a bone fragment is created, a cut between the bone fragment (the primary bone zone) and the remainder of the cranium (the secondary bone zone) is present.
Several methods of alignment and fixation of primary and secondary bone zones are known. Traditional techniques involve the use of several pieces of filament, such as wire, that are tied after being threaded through holes drilled obliquely through the outer cortex to the cut surface of both bone zones. Precise alignment of the two zones can be difficult and the technique can be cumbersome.
Commonly, the zones of bone can be aligned and fixated with a system of plates and screws (U.S. Pat. Nos. 5,372,598; 5,413,577; and 5,578,036). A plate made of metal or other substance can be fixated to the outer cortex of the primary bone zone with screws whose penetration of the bone can be limited to the outer cortex. With three or more plates attached to the primary bone in such a way that the plates protrude beyond the edges of the primary bone zone, the primary bone zone can be introduced into a defect and aligned to the outer cortex of the secondary bone zone without danger of the primary bone zone falling too deeply into the defect in the secondary bone zone and exerting pressure on the underlying tissue such as the brain. Fixation can then be achieved by employing additional screws fixating the plates to the outer cortex of the secondary bone zone. Plates and screws systems allow for the alignment and fixation of the zones, while preventing the primary bone zone from falling below the level of the secondary bone zone without actually introducing a component of the device below the secondary bone zone. A plate with a spring clip extension has been described (U.S. Pat. No. 5,916,217). Plate and screw systems can be expensive and time consuming to use.
Devices that align the two bone zones by way of compressing them between the two disks positioned along the inner and outer cortex have been described. (Foreign Patents: DE 19603887C2, DE 19634699C1, DE 29812988U1, EP 0787466A1.) A pin connects the two disks aligning and securing two bone zones. These devices introduce foreign material that is left below the inner cortex, and they do not protect the underlying tissue from compression during the installation procedure.
Devices that fixate bone zones using friction forces created by a cam without a component that extends below the inner cortex are known and described (Patent DE 19634697C1). These devices also do not protect the brain from compression during the installation procedure.
Intramedulary pins are well known in the orthopedic fields for alignment of long bones. Such pins have also been described for cranial fixation (U.S. Pat. No. 5,501,685); however, the bone zones can not be aligned in three dimensions with this technique.
There is a need for an alignment and fixation device that is simple and rapid to use, versatile, and ultimately cost effective. There is also need for easily usable clip structure.
One object of the invention is to provide a device and instruments for its use and installation that aligns one cortex of a primary zone with one cortex of a secondary bone zone without extending to the opposing cortex, and which accurately fixates the bone zones to each other. When used in the field of neurosurgery, the device is applied to the primary bone zone and it aligns the outer cortex of the primary bone zone with the outer cortex of the secondary bone zone; it prevents the primary bone zone from entering the cranial cavity; and it provides fixation of the two bone zones.
One fixation feature of the invention relies on the principle that the device is fixated to the primary bone zone and the fixation feature grips the secondary bone zone by means of bowed strut elements engaging the soft areas of the medullary space, irregularities along the cut surface, or a slot cut into the cut surface of the secondary bone zone. Another feature is the use of a bowed strut or tab extension to support a projection or projections to be driven into the edge of a primary bone zone to retain the clip in anchored position.
The invention provides an improved clip meeting the above need or needs.
As will be seen, the preferred clip is configured to interconnect primary and secondary bone zones having edges spaced apart by a gap, the clip comprising
a) a first tab to extend over a surface of the secondary bone zone, above a level defined by that surface, and
b) an extension of the tab projecting below said level, and a first projection carried by the extension for penetrating the primary bone zone below said first level,
c) said extension having bowed configuration, to enable forcible driving of the projection, to effect said penetrating.
The extension or strut may typically have S-shape to provide a spring carrying the first projection to be driven into bone tissue.
As will be seen, a second projection may be provided to be carried by the other tab, and configured to engage the secondary bone zone at the edge thereof.
In this regard, the second projection is typically to be located beneath the first tab; and the first projection is to be driven generally parallel to that tab and forwardly from a part of the bowed tab extension below tab level, and it preferably has a sharp terminal to enable penetration of diploe.
A further object is to provide the second projection to have a sharp terminal, and to extend at an acute angle toward the plane of the first tab, in order to resist removal relative to the secondary bone zone.
Yet another object is to provide another second projection carried by the tab in sidewardly spaced relation to the first mentioned second projection, and configured to engage the secondary bone zone at the edge thereof.
An additional object is to provide S-shaped spring support of both first and second projections, to enhance their functioning and assist their initial and subsequent positioning in the gap between the two bone zones. The positioning of the first projection supported independently of the second projection or projections, enables driving of the first projection without effecting the positioning and functioning of the second projection or projections.
An additional object is to provide a plate or flap defining the primary bone zone, and to provide multiple of the clips having their first projections penetrating the primary bone zone at different edges thereof, below a surface defined by the plate or flap.
The method of using the clip as referred to includes orienting the first projection to align with an edge of the primary bone zone and driving the first projection into the primary bone zone at the edge thereof, by driving said bowed extension which provides an anvil, and attaching the tab to said surface.
In this regard, the method may include effecting penetration of the edge of the secondary bone zone by a second projection in an angular direction toward the plane of the tab. The bowed or S-shapes of the independent supports for either or both the first and second projections provide enhanced spring effect, and aid in initial positioning of the projections, as well as their independent clip anchoring functions at multiple locations.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: